This invention relates to an improved inverse emulsion to inhibit brittle lutite hydration. The improved inverse emulsion is made up of the following elements: special-type diesel oil; viscosity agent with thermostabilizing properties acting as the main controller of filtration properties and as a secondary emulsifier; main emulsifying agent acting as well as a wetting agent for the thickening solids; calcium chloride brine; thickening agent; gelatinizing agent and hydrated calcium hydroxide.
Conventionally, a drilling fluid whose consistency resembles that of a lubricating oil, is used in a circulating system with rotary drilling mechanisms. The fluid is pumped into the well through the drilling bit, which it lubricates and cools, and then it is returned to a hydraulic-fill dam on the surface. In this way it removes cuttings and carries them out of the well to the surface, where thick particles are removed, leaving the fluid in good condition to be used again in a continuous-circulation process.
Reasons for using drilling fluids are varied and complex. One of the main reasons for their use is the desire to exert an adequate hydrostatic pressure in order to prevent gas leaks and thus avoid well fires.
Taking into consideration that hydrostatic pressure depends, to a large extent, on a fluid's specific gravity, it may be increased, as indicated in the present invention, through the addition of a heavy material such as barite. On the other hand, drilling fluid should have an adequate viscosity, i.e., it should be viscous enough to remove cuttings. However, at the same time, it should be pumpable and allow heavy particles to settle out in the hydraulic-fill dams, so that it may be used again.
An important property of the drilling fluid is that in case of a temporary shutdown, the fluid's gelling capabilities should be enough to prevent suspended cuttings from settling out since, otherwise, those cuttings would stick to the well's shaft and obstruct restarting operations and their final removal from the fluid. Therefore, both its fluid viscosity and its gelling capability or gelationusness, in case of a drilling or repair work shutdown, are of paramount importance. Consequently, the fluid should maintain cuttings suspended until work is resumed. This is known as a fluid's thixotropic property or gel intensity. Such a property may be enhanced through the addition of a bentonitetype clay or similar substances, as in the present invention where bentonite, previously reacted with ammonium quaternary salts, is used.
During oil well drilling, the drill frequently encounters brittle lutites or water-base muds that hydrate when they are in contact with water, causing landslides or hole instability. Thus fluids that act as agents to inhibit brittle lutite hydration have been developed and it has been known that inverse emulsions provide the best results.